Currently, optical disk devices (e.g. DVD disk apparatus) that mount an optical pickup (including an objective lens) for recording a signal onto, or reproducing a signal from, an optical data record medium (e. g. optical disk such as DVD disk) are in increasing demand.
These optical disk devices have an objective lens driving apparatus for driving an objective lens in response to a control signal and performing focusing control and tracking control.
This invention relates to an objective lens driving apparatus, and particularly to the configuration of a support printed board and its periphery for restraining the winding of a focusing coil or a tracking coil of the objective lens driving apparatus.
Japanese Laid-open Public Patent Application Hei 5-342607 describes a conventional objective lens driving apparatus having a support printed board for restraining winding of a focusing coil or a tracking coil.
The configuration will be explained hereinafter.
FIG. 14(a) shows a front view of the conventional objective lens driving apparatus described in the Official Gazette of Japanese Laid-open Public Patent Application Hei 5-342607.
FIG. 14(b) shows a bottom view of the conventional objective lens driving apparatus described in the Official Gazette of Japanese Laid-open Public Patent Application Hei 5-342607.
FIG. 14(c) shows a left side view of the conventional objective lens driving apparatus described in the Official Gazette of Japanese Laid-open Public Patent Application Hei 5-342607.
In FIG. 14, 1 is an objective lens and 2 is a lens holder to which the objective lens 1 is attached. A focusing coil 3 for driving the objective lens 1 in the focusing direction (a direction of the arrow shown in FIG. 14, that is, the same direction as that of the optical axis of the objective lens 1) and a tracking coil 4 for driving the objective lens 1 in the tracking direction (a direction of the arrow shown in FIG. 14) are wound around the lens holder 2.
Two support printed boards 5 are fixed at two positions indicated by the tip of the arrow pointing to lens holder 2.
The starting ends and the terminating ends of the focusing coil 3 and the tracking coil 4 are restrained by winding a few turns along coil restraining parts, which are located in the vicinity of the front end parts of the support printed boards 5 which protrude from the top surface and the bottom surface of the lens holder 2.
A fixed member 6 is composed of a printed board and referred to as an act printed board. As shown in the left side view, the act printed board 6 has four patterns, each pattern having a land part and a through hole formed in the center or the periphery of the land part at one end. A support block 7 has a recessed part injected with damper material 8 therein and four through holes formed in the recessed part. The act printed board 6 and the support block 7 are fixed so that four through holes of the act printed board 6 and four through holes of the support block 7, respectively, are placed coaxially.
Each end of four suspension wires 9 made of conductive metal wire are fixed to the act printed board 6 by soldering through the through hole of the act printed board 6 and the through hole of the support block 7 at one end, and fixed to the coil restraining part of the support printed board 5 by soldering at the other end.
With the above-mentioned configuration, it is possible to obtain a conductive path which starts from one of the patterns of the act printed board 6, through 2 suspension wires 9 connected thereto, a land part of the support printed board 5 connected to the suspension wire 9, the focusing coil 3 connected to the land part of the support printed board 5, other land part of the support printed board 5 connected to the other end of the focusing coil 3, other suspension wire 9 connected to the other land part of the support printed board 5, and returns to the other patterns of the act printed board 6 connected to the other suspension wire 9.
By feeding current of a focusing control signal through this path, focusing control of the objective lens 1 is achieved.
Similar to the focusing control signal, by feeding current of a tracking control signal through the conductive path containing the other two patterns of the act printed board 6, the other two suspension wires 9, the other two land parts of the support printed board 5, and the tracking coil 4, tracking control of the objective lens 1 is achieved.
Furthermore, the support block 7 is fixed to a yoke 10 at the position as shown in the figure.
The lens holder 2 is supported by four suspension wires 9 so as to be located at the center between permanent magnets 11 and 12.
A magnetic circuit consisting of the permanent magnets 11 and 12, and the yoke 10 provided as an adjunct with the permanent magnets 11 and 12 generates a substantially uniform magnetic field in the vicinity of the focusing coil 3 and the tracking coil 4.
By feeding a focusing control signal to the focusing coil 3 within the uniform magnetic field, Lorentz force is generated, thereby producing a torque for driving the lens holder 2 in the focusing direction.
Likewise, by feeding a tracking control signal to the tracking coil 4 within the uniform magnetic field, Lorentz force is generated, thereby producing a torque for driving the lens holder 2 in the tracking direction.
As four suspension wires 9 are made of flexible metal wire, the lens holder 2 undergoes displacement due to the above-mentioned torque actuation.
Moreover, in the instance in which the focusing coil 3 and the tracking coil 4 are wound by an automatic winder, parts of the support printed board 5 are configured to protrude from the lens holder 2 and the parts neighboring the front ends of the protruding support printed board act as coil restraining parts, thereby facilitating restraint of the starting ends and the terminating ends of windings.
The objective lens driving apparatus is required to improve tracking sensitivity for high-speed playback. As a solution, it is effective to reduce the weight of the movable body. Specific measures are thinning of the lens holder and weight reduction in the support printed board.
However, weight reduction causes rigidity degradation of the movable body, resulting in the deterioration of the high-order resonance characteristic of the objective lens driving apparatus. Although thinning of the lens holder and weight reduction in the support printed board are effective in improving tracking sensitivity, these members become less integrated. As a result, the coil restraining part of the support printed board which protrudes from the lens holder has a separate vibration mode at high frequencies.
For that reason, with respect to the vibration characteristic of the objective lens driving apparatus, undesired resonance and disturbance in phase occurs, and tracking performance of the objective lens driving apparatus for the optical data recording medium deteriorates. Further, there is the possibility of consuming unnecessary electricity for tracking.
On the other hand, in order to facilitate the arrangement of the starting ends and the terminating ends of the coils wound by an automatic winder, it is desirable to configure the coil restraining part of the support printed board to protrude from the lens holder as mentioned above.
An object of the present invention is to provide an inexpensive and easily manufacturable objective lens driving apparatus which is excellent in tracking sensitivity and free from the undesired resonance mode.
Another object of the present invention is to provide an inexpensive manufacturing method for manufacturing an objective lens driving apparatus which is excellent in tracking sensitivity and free from the undesired resonance mode without adding new processes.